(a) Field of the Invention
The present invention relates generally to solar panel testing and, more particularly, to an apparatus for providing uniform light intensity during solar panel testing.
(b) Description of Related Art
Spacecrafts use solar panels to provide electrical power for spacecraft operation and the charging of batteries. A solar panel is made from a number of individual photovoltaic cells, which produce electrical current in response to solar energy. Reliability in the testing of solar panels is very important to both solar panel manufacturing and spacecraft operation.
Currently, solar panel reliability and performance are characterized using a test configuration such as a large area pulse solar simulator (LAPSS). Often there is a fine line between acceptable and unacceptable panels. Therefore, tests used to characterize cell performance must be precise and consistent. Precision and consistency are the keys for determining manufacturing yield and field reliability of the solar panels. Manufacturing yield refers to the number of tested and acceptable solar panels that were produced in a production run of a large number of solar panels. Additionally, correlation and repeatability between test results of different test configurations is desirable. That is, if a particular solar panel fails in a first test configuration, it should also fail in a second test configuration.
Advances in solar panel and solar cell technology have yielded larger and more efficient solar panels. These advances make precision and consistency in product testing even more important because a small difference in light intensity can yield a significant difference in current produced by the solar panel.
A test configuration such as a LAPSS system uses light sources, such as Xenon flash tubes, a series of baffles, and a test bed for measuring the performance of a solar panel. When the light sources illuminate the solar panel, the test bed reads the voltages and currents produced by the panel. A uniform light source is required to prevent cell "hot spots" where light intensity is non-uniformly high and "cold spots" where light intensity is non-uniformly low. Hot spots on the panel occur on the portion of the solar panel that is directly aligned with the light source. Conversely, cold spots occur on the portion of the solar panel that is near the fringe of the light source. Hot spots and cold spots make accurate and repeatable measurements impossible due to the non-uniform illumination of the solar panel. Currently, light sources, such as those used in a LAPSS system, provide reasonably uniform light intensity, but do not take any measures to provide uniform intensity. Additionally, as solar panel sizes and efficiency increase, current test configurations are unable to illuminate the cell with the required light uniformity, thereby magnifying the problems of test reliability and repeatability. Many test configurations require a large panels under test to be moved many times during testing to illuminate sections of the panel with a reasonably uniform light source. The requirement of moving a panel under test limits test accuracy and repeatability, which increases manufacturing cost and time.
The advantages of a highly uniform light intensity device can be readily appreciated. Such a source would increase the reliability and repeatability of test results, thereby accurately predicting the field reliability of solar panels.